| 1891 MLB season | |
|---|---|
| League | American Association (AA) National League (NL) |
| Sport | Baseball |
| Duration | April 8 – October 6, 1891 (AA) April 22 – October 3, 1891 (NL) |
| Number of games | 140 |
| Number of teams | 17 (8 active per league, 9 AA total) |
| Pennant winner | |
| AA champions | Boston Reds |
| AA runners-up | St. Louis Browns |
| NL champions | Boston Beaneaters |
| NL runners-up | Chicago Colts |
The 1891 Major League baseball season was contested from April 8 through October 6, 1891. It was the final season for the American Association (AA), with the Boston Reds winning the AA pennant. In the National League (NL), in operation since 1876, the Boston Beaneaters won the NL pennant. There was no postseason. The Reds, following the 1890 Brooklyn Bridegrooms consecutive pennant wins 1889–1890 in different leagues, also followed such a feat, winning the since folded Players' League's 1890 pennant and becoming the second and last team to win consecutive pennants in different leagues.
This was the first season since 1883 which saw no postseason, due to a breakdown in relations between the American Association and National League prior to the start of the season. The next championship series would take place the following season in a unique split season format, due to negotiations during the merger of the AA into the NL.
The 1891 season saw the aftermath of the single-season Players' League disbanding during the offseason, with most teams either folding or merging with existing American Association and National League teams; the Boston Reds and Philadelphia Athletics would join the AA for the 1891 season, with the latter replacing the financially struggling original AA Philadelphia Athletics.
The unstable American Association would see that 1891 would be its final season, before merging into the National League the following season; the four clubs that would continue on were the Baltimore Orioles, Louisville Colonels, St. Louis Browns, and Washington Statesmen. The other four AA clubs, the Boston Reds, Columbus Solons, Milwaukee Brewers, and Philadelphia Athletics), saw their owners paid $135,000 (equivalent to $4,724,500 in 2024) and their players dispersed to the surviving twelve clubs.